1. Field of the Invention
The present invention relates to an engine with a supercharger to increase intake pressure of the engine, more specifically to a control device of the engine with the supercharger including an exhaust gas recirculation apparatus configured to return part of exhaust gas of the engine to the engine and controlling the exhaust gas recirculation apparatus and others in accordance with an operating condition of the engine.
2. Related Art
Heretofore, this type of technique is, for example, applied to an engine for an automobile. An exhaust gas recirculation (EGR) apparatus is arranged to allow part of exhaust gas discharged after combustion from a combustion chamber of the engine to an exhaust passage to flow as EGR gas into an intake passage via an EGR passage, so that the exhaust gas is mixed with intake air flowing in the intake passage and returns to the combustion chamber. The EGR gas flowing in the EGR passage is regulated by an EGR valve provided in the EGR passage. This EGR can reduce mainly nitrogen oxide (NOx) in the exhaust gas and improve fuel consumption during a partial load operation of the engine.
Exhaust gas from the engine contains no oxygen or is in an oxygen lean state. Thus, when part of the exhaust gas is mixed with the intake air by EGR, the oxygen concentration of the intake air decreases. In a combustion chamber, therefore, fuel burns in a low oxygen concentration. Thus, a peak temperature during combustion decreases, thereby suppressing generation of NOx. In a gasoline engine, intake negative pressure is increased without increasing the content of oxygen in the intake air by EGR, so that it is possible to reduce pumping loss of the engine.
Herein, recently, it is conceivable to perform EGR in an entire operating region of the engine in order to further improve fuel consumption. Realization of high EGR rates is thus demanded. To realize the high EGR rates, it is necessary for conventional arts to increase an internal diameter of an EGR passage or increase an opening area of a flow passage provided by a valve element and a valve seat of an EGR valve.
Meanwhile, it is also known to provide the EGR apparatus to an engine equipped with a supercharger. Japanese Patent No. JP5056953B2 (WO2011/111171A1) discloses a supercharger-equipped engine of this type and a low pressure loop EGR apparatus. The supercharger includes a turbine placed in an exhaust passage and a compressor placed in an intake passage and driven by the turbine. This low pressure loop EGR apparatus includes an EGR passage provided between the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and an EGR valve provided in the EGR passage. Further, an intake bypass passage is provided between the intake passage downstream of the compressor and the intake passage upstream of the compressor, and provided with an air bypass valve (ABV). When the engine is in deceleration operation (when a throttle valve provided in the intake passage is closed) from a supercharging region in which the supercharger is operated, the ABV is opened to prevent generation of surge and concurrently the EGR valve is closed. Thus, the pressure in the intake passage downstream of the compressor is decreased and the EGR gas flowing in the intake passage is reduced so as to reduce the EGR gas flowing in the intake bypass passage and the compressor. Thereby, the EGR gas is prevented from being highly concentrated. Herein, the “surge” means a phenomenon in which gas flowing in the compressor of the supercharger and the intake passage is strongly oscillated in the flow direction. In a case that this oscillation goes extreme, that could cause flow back of the gas from an outlet to an inlet of the compressor, intermittent unusual sound, and oscillation of pipes of the compressor and the intake passage.